Boiling water reactor nuclear power plant with alcohol injection

ABSTRACT

A nuclear power plant is provided including a BWR, a reactor cooling system cooling the BWR, an HWC hydrogen injection system connected to the reactor cooling system and an alcohol injection system connected to the reactor cooling system. Methods for providing methanol and hydrogen are also provided.

This application is a divisional of U.S. patent Ser. No. 11/904,657,filed Sep. 28, 2007, and which is hereby incorporated by referenceherein.

The present invention relates generally to nuclear power plants and moreparticularly to nuclear power plants with boiling water reactors (BWRs).

BACKGROUND

Oxidation caused by oxidants such as oxygen and hydrogen peroxide in thecooling water of BWRs can cause stress corrosion cracking (SCC) onreactor components, and cause corrosion of the zirconium alloy claddingof the fuel pins. Known SCC reduction strategies for reactor componentssuch a reactor pressure vessel (RPV) internals of BWRs include noblemetals chemistry addition (NMCA) and hydrogen water chemistry (HWC).These SCC reduction strategies can reduce SCC of internals, but mayincrease corrosion of the fuel pin cladding.

NMCA methods are described for example in U.S. Pat. Nos. 5,818,893,5,904,991 and 6,793,883, and as defined herein NMCA may include bothoff-line or on-line addition of noble metals.

HWC used with NMCA is described in the background section of U.S. PatentApplication Publication No. 2005/0018805, which then also describesapplication of a reductive nitrogen compound such as hydrazine incombination with hydrogen. Application of an alcohol such as methanolwith hydrazine is also disclosed. DE 100 30 726 describes application ofphotocatalytic substances for depositing on reactor internals, andmentions the injection of hydrogen or methanol.

Application of methanol to reduce oxidizing effects is described in U.S.Patent Application Publication No. 2005/0135542, as well as in thepublication entitled “Study of the Methanol Injection in Reactor Waterin Reactor Water of BWR Plants” by Saneshige et al. presented at theProc. Symp. on Water Chemistry and Corrosion of Nuclear Power Plants inAsia, Oct. 11-13, 2005, Gyeongju, Korea.

Shut down and then start-up of BWRs can occur at regular intervals, forexample, every one to three years, and present very different waterchemistries than during normal operation. As discussed, for example, inthe publication “The First Application of Hydrogen Water Chemistryduring Start-up for Mitigation of SCC initiation in Tokai-2 BWR” byTakiguchi and Otoha, oxidant concentration in reactor water is highduring start-up. The publication describes the addition of HWC duringstart-up via an additional hydrogen injection system.

U.S. Patent Publication No. 2005/0018805 also describes adding hydrogenand a reductive nitrogen compound during start-up and shut-down.

SUMMARY OF THE INVENTION

While the use of HWC during start up is known, this procedure hasseveral drawbacks. Contact of the hydrogen with air pockets which can bepresent during start-up needs to be avoided to prevent the possibilityof an explosive reaction. In addition, the use of HWC during start-uphas several other drawbacks listed in the publication “The FirstApplication of Hydrogen Water Chemistry during Start-up for Mitigationof SCC initiation in Tokai-2 BWR” such as not being able to maintain aproper target concentration during certain start-up operationconditions. The varying conditions during both start-up and shut-down,such as a varying amount of coolant circulating through the reactor andvarying reactor temperatures, thus make proper dosing of gaseoushydrogen exceedingly difficult. Furthermore, hydrogen injection may notbe possible at other times, for example during repair or malfunction.

Noble metals often also begin to have reduced effect as catalysts duringcertain periods, for example, when operating at temperatures of 250degrees Celsius or below and when hydrogen injection is not available.During start-up and shut-down temperatures fall below these levels andhydrogen injection is complex.

An object of invention is to reduce oxidation and reduce corrosion onreactor core components and fuel claddings during periods when HWC isnot available or desirable, for example, during malfunction of the HWCinjection system or start-up and shut-down of the reactor. Anotheralternate or additional object of the present invention is to providefor safer, less expensive and/or less complex oxidation reduction.

The present invention provides a nuclear power plant including a BWR, areactor cooling system cooling the BWR, an HWC hydrogen injection systemconnected to the reactor cooling system, and an alcohol injection systemconnected to the reactor cooling system.

By providing a separate alcohol injection system in addition to thehydrogen injection system, the use of hydrogen or alcohol for variousoperating regimes, for example, during start-up and shut-down as opposedto normal operating conditions, advantageously can be controlled.Alcohol as well advantageously can be provided as a back-up injectionsystem at times when the hydrogen injection system is inoperable orotherwise not available. The use of alcohol, which can be provided inliquid form and does not explode when in contact with air pockets, alsoadvantageously improves safety, requires less careful monitoring andrequires less complex delivery equipment.

Additional components, such as a reductive nitrogen compound injectionsystem, and NMCA injection system advantageously can be provided aswell.

The present invention also provides a method for operating a nuclearpower plant including providing an alcohol to a BWR during start-up orshut-down operation.

Alcohol has typically not been considered suitable for start-up orshut-down, since, as described in U.S. Patent Publication No.2005/0018805, the radiation levels during start-up and shut down were atlower intensities and alcohols were generally considered useful whengamma radiation was present. However, the present invention recognizesthat using alcohol instead of HWC during start-up or shut-downadvantageously permits some oxidation reduction, while reducing dangersrelated to explosions and simplifying equipment requirements. Theadditional alcohol injection system may be added on to existing BWRnuclear power plants or provided to new power plants, and may beconnected to the primary coolant in the reactor via, for example, thereactor water clean up system (CUW), emergency core cooling system(ECCS), primary loop recirculation system (PLR), or control rod drivecooling system (CLD).

Advantageously, hydrazine or another reductive nitrogen compound can beprovided to the BWR primary cooling circuit at the same time as thealcohol and hydrogen to improve the overall oxidation reductionperformance of the additives.

The present invention also provides a method for operating a nuclearpower plant including providing both hydrogen and an alcohol to a BWRprimary cooling circuit during normal operation of the power plant.

In the past, methanol was seen as an alternative to hydrogen. Byproviding both hydrogen and methanol, the mixture of hydrogen andmethanol can be altered as desired to provide adequate oxidationreduction. Moderate negative electrochemical potential values can beachieved (slightly below −240 mV), while still providing oxygen reducingspecies of both types. Moreover, back-up protection can thus beprovided, for example when the amount of stored hydrogen for HWC isrunning low, or the hydrogen injection fails, methanol can be dosed withthe hydrogen to reduce the amount of hydrogen being used.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will be described withrespect to the drawing in which:

FIG. 1 shows one embodiment of a nuclear power plant according to thepresent invention;

FIG. 2 shows more details of hydrazine and methanol injectors of theembodiment of FIG. 1;

FIG. 3 shows quantities of hydrogen and methanol to provide anequivalent effect of 1.2 ppm hydrogen in a BWR 900 MWe reactor core; and

FIG. 4 shows the effect of polarization on oxidation and hydrogenpick-up (HPU) of zirconium in water at 315-350° C.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows schematically one preferred embodiment of a BWR nuclearpower plant 10 according to the present invention. Nuclear power plant10 has a BWR 20 having a core 22 with a plurality of fuel rods having,for example, uranium dioxide fuel in zirconium alloy tubes, a downcomer26 and a riser 28, shown schematically. Downcomer 26 is connected to aprimary coolant inlet 24, which receives water from a primary coolantline 30. Core 22 heats water from the primary coolant line 30, which hasa hot leg 32 providing steam to a turbine 40 driving a generator 42. Acondenser 44 condenses the steam into water, which exits the condenserinto a cold leg 34 of coolant line 30, and is pumped back to the inlet24 and downcomer 26.

A control rod drive cooling system (CLD) 50 can be provided to cool adrive for control rods inserted into core 22. An HWC hydrogen injector60 can inject hydrogen into cold leg 34, and an NMCA injector 62 canprovide a noble metal for example, platinum, into cold leg 34 as well,so that the reactor 20 experiences HWC and NMCA during normal periods ofoperation.

An ECCS 70, PLR 80 and CUW 90, all shown schematically, may also beprovided.

The specific embodiment of FIG. 1 provides a methanol injector 100 and ahydrazine injector 110, which are connected to CUW 90 for example,downstream of a CUW pump. Methanol and hydrazine thus can be injectedinto water entering cold leg 34 of primary coolant line 30 via CUW 90,and can circulate through reactor 20. Cooled down CUW sample lines canalso be used to receive injector 100, 110 fluids. Injectors 100, 110also could be located at the ECCS 70, PLR 80 or CLD 50. Alternately, anexisting injector, such as one used for sodium-24 injection andconnected to CUW 90, could also be modified to use as an injector 100 or110. The preferred location is past any resin beds.

The amount of methanol and hydrazine injected can be controlled by acontroller 120, which can receive an input from one or more sensors 130,for example, monitoring the concentration of methanol, hydrazine orhydrogen in downcomer 26. Pre-set quantities of methanol can be injectedconsidering for example hydrogen values in downcomer 26. Sensors 130 canalso measure an electrochemical potential (ECP) of one or morecomponents of reactor 20 or core 22, for example the cladding of thefuel pins.

FIG. 2 shows one embodiment of methanol injector 100 and hydrazineinjector 110, which can include tanks 104, 114, respectively, connectedto piping of CUW 90. Metering pumps 102, 112 can release, respectively,methanol and/or hydrazine into CUW 90, and can be controlledindividually via controller 120. Controller 120 can be the samecontroller controlling start-up and shut-down operations or a separatecontroller. Alternatively, in a gravity-assisted injector embodiment,the amount of methanol or hydrazine provided can be controlled byturning on and off the valves, with the tanks suspended above thepiping.

While methanol is preferred, other alcohols may be delivered, includingethanol and propanol, which are also preferred. However, formic acid,formaldehyde and acetaldehyde are other examples of suitable alcohols.

While hydrazine is the preferred reductive nitrogen compound, othercompounds such as ammonia (NH3) are also possible.

In one preferred method of the present invention, alcohol is injectedinto the primary coolant to establish an alcohol concentration from 0.1to 300 μmol/kg (≈0.0032 to 9.6 ppm for methanol) in downcomer 26 duringstart-up or shut down, or during another time when HWC 60 is notoperating, for example when HWC is malfunctioning. Most preferably, thealcohol concentration is less than 10 μmol/kg.

The hydrazine also is preferably provided during shut-down and start-upinto the primary coolant to establish a maximum hydrazine concentrationof 300 μmol/kg in downcomer 26.

In another preferred method of the present invention, it is advantageousto use both hydrogen and methanol injection during normal operation. Itis also possible to use all of the hydrogen-containing chemicalinjectors, such as for hydrogen, methanol and hydrazine, at the sametime. The various hydrogen containing chemical injectors can be phasedin or phased off due to various phases of operation. Preferably, thecombination of the hydrogen containing chemicals added should,stoichimetrically equivalent with respect to hydrogen, be maintainedaround or below the equivalent of 10 μmol/kg methanol. The metering-inof hydrogen or alcohol or hydrazine, after exceeding a certain limit maylead to several disadvantageous results, and thus most preferably thelimit of all of the injected hydrogen-containing chemicals does notexceed the equivalent of 300 μmol/kg methanol

FIG. 3 presents the quantities of methanol to be injected in feed-waterof a 900 MW electric standard BWR during normal operation so that theeffect in the reactor core would be the one provided by an injection infeed water of 1.2 ppm hydrogen. It is an illustration of stoichimetriccalculations involving only two components: methanol and hydrogen.Diffusion of hydrogen in the downcomer and carry over of hydrogen bysteam are considered in the calculations of FIG. 3. Column 1 thus is thefeed-water concentration FC of hydrogen provided by HWC 60, column 2 thepredicted downcomer concentration RC during normal operation, and column3 the predicted core concentration CC of hydrogen during normaloperation. Column 4 shows the differential hydrogen predicted as missingfrom the core as the hydrogen concentration in the feed water decreasesand column 5 the equivalent methanol which must be provided tocompensate. Columns 6, 7 and 8 then show the desired methanolconcentrations in the feed water, downcomer and core respectively tostoichimetrically compensate for the reduced hydrogen injection by HWC60. Similar calculations can be performed when three or more componentsare involved and one is replacing the other in successive steps (whenone decreases another one increases).

In addition, methanol is more effective than hydrogen in reductionhydrogen peroxide concentrations and in producing negative ECP values,as discussed in, for example, the publication “Reasons and Criteria forSelection of Methanol as an Alternative to Hydrogen for BWR Plants”presented at the 5th International Workshop on LWR Coolant WaterRadiolysis and Electrochemistry, San Francisco, October 2004 by BernhardStellwag and Wilfried Ruehle, hereby incorporated by reference herein.Experimental data in radiation field shows that the hydrogen peroxide isabout a factor of two lower with methanol than with hydrogen at the samemolal oxygen ratios. Also, the methanol is about three times moreeffective than hydrogen to reach the same ECP as a function of oxygenmolal ratio.

Sensors 130 could be provided to ensure exact downcomer concentrationsRC via monitoring of the hydrogen and the methanol concentrations in thedowncomer 26.

Examples of preferred mixed use, with three injectors 100, 110, 60include:

A. injection of methanol at a constant level, while increasing hydrazineinjection and decreasing hydrogen injection (shut-down);

B. methanol and hydrazine injection both increasing while hydrogeninjection is absent (beginning of start-up);

C. methanol injected at a constant level with hydrazine still increasingand hydrogen injection absent (end of start-up);

D. methanol injection constant with hydrazine decreasing and hydrogenincreasing (beginning of normal operation of HWC or NMCA);

E. methanol injection increasing or decreasing to compensate for loss ofhydrogen injection during normal operation; and

F. methanol injection increasing or decreasing to compensate for effectson ECP during on-line NMCA injection.

In FIG. 4, a large body of research is summarized showing that zirconiumhydrogen pick-up (HPU) or hydrogen pick-up fraction (HPUF) and oxidationincreases dramatically, if the ECP of the fuel pin becomes cathodic(negative) and goes below −300 mV. ECP levels of −300 mV or higher thusare preferred as far as fuel operation is concerned. The concentrationin feed-water of the combinations of all reducing agents(hydrogen+methanol+hydrazine) applied to a BWR can be such to provide areducing environment characterized by an ECP potential against the Pt(platinum) reference electrode around or higher than −300 mV (e.g. −260mV). To protect both the BWR reactor internals and also maintain anincrease fuel operation margin, ECP potential against the Pt (platinum)reference electrode around or higher than −300 mV (e.g. −260 mV),preferably should be maintained, rather than −500 mV usually imposed byoperators to minimize the SCC of internals.

In the present invention, it is preferable to use methanol.Alternatively, other suitable alcohols may be used including, forexample, ethanol or propanol, or a mixture of any of these.

In the preceding specification, the invention has been described withreference to specific exemplary embodiments and examples thereof. Itwill, however, be evident that various modifications and changes may bemade thereto without departing from the broader spirit and scope ofinvention as set forth in the claims that follow. The specification anddrawings are accordingly to be regarded in an illustrative manner ratherthan a restrictive sense.

1. A method for operating a nuclear power plant including a boilingwater reactor, lines flowing to the boiling water reactor, a hydrogeninjector for injecting hydrogen into at least one of the lines and analcohol injector for injecting an alcohol into at least one of thelines, the method comprising: injecting hydrogen from the hydrogeninjector into at least one of the lines flowing to the boiling waterreactor and injecting the alcohol from the alcohol injector into atleast one of the lines flowing to the boiling water reactor duringnormal operation of the power plant; and compensating for a loss ofhydrogen by injecting an amount of alcohol stoichiometrically equivalentto the amount of the loss of hydrogen.
 2. The method as recited in claim1 wherein the alcohol is methanol.
 3. The method as recited in claim 1wherein the alcohol includes at least one selected from a groupincluding methanol, ethanol and propanol.
 4. The method as recited inclaim 1 wherein the alcohol and hydrogen are injected at a same time. 5.The method as recited in claim 1 further comprising providing areductive nitrogen compound to the boiling water reactor.
 6. The methodas recited in claim 1 wherein the alcohol is injected into one of areactor water cleanup system, an emergency core cooling system, acontrol rod driving system or a primary loop recirculation system. 7.The method as recited in claim 1 wherein the compensating is controlledby a controller.
 8. The method as recited in claim 1 wherein the alcoholinjected establishes an alcohol concentration from 0.1 to 300 μmol/kg ina downcomer of the boiling water reactor.
 9. The method as recited inclaim 8 wherein the alcohol concentration is from 0.1 to 10 μmol/kg inthe downcomer of the boiling water reactor.
 10. The method as recited inclaim 5 wherein the reductive nitrogen compound injected is hydrazine,the hydrazine providing up to a maximum hydrazine concentration of 300μmol/kg in a downcomer of the boiling water reactor.
 11. A method foroperating a nuclear power plant including a boiling water reactor, linesflowing to the boiling water reactor, a hydrogen injector for injectinghydrogen into at least one of the lines, an alcohol injector forinjecting an alcohol into at least one of the lines and a reductivenitrogen compound injector for injecting a reductive nitrogen compoundinto at least one of the lines, the method comprising, during shut-down:injecting the reductive nitrogen compound from the reductive nitrogencompound injector into at least one of the lines flowing to the boilingwater reactor at an increasing quantity; injecting the hydrogen from thehydrogen injector into at least one of lines flowing to the boilingwater reactor at a decreasing quantity; and injecting the alcohol fromthe alcohol injector into at least one of the lines flowing to theboiling water reactor at a constant quantity; wherein the reductivenitrogen compound, the hydrogen and the alcohol are injected duringshut-down such that a reducing environment characterized by anelectrochemical potential higher than −300 mV is provided in the boilingwater reactor.
 12. A method for operating a nuclear power plantincluding a boiling water reactor, lines flowing to the boiling waterreactor, a hydrogen injector for injecting hydrogen into at least one ofthe lines, an alcohol injector for injecting an alcohol into at leastone of the lines and a reductive nitrogen compound injector forinjecting a reductive nitrogen compound into at least one of the lines,the method comprising, during a beginning of the start-up: injecting thereductive nitrogen compound from the reductive nitrogen compoundinjector into at least one of the lines flowing to the boiling waterreactor at an increasing quantity; and injecting the alcohol from thealcohol injector into at least one of the lines flowing to the boilingwater reactor at an increasing quantity; wherein no hydrogen is providedfrom the hydrogen injector into any of the lines; wherein the reductivenitrogen compound and the alcohol are injected during the beginning ofstart-up such that a reducing environment characterized by anelectrochemical potential higher than −300 mV is provided in the boilingwater reactor.
 13. A method for operating a nuclear power plantincluding a boiling water reactor, lines flowing to the boiling waterreactor, a hydrogen injector for injecting hydrogen into at least one ofthe lines, an alcohol injector for injecting an alcohol into at leastone of the lines and a reductive nitrogen compound injector forinjecting a reductive nitrogen compound into at least one of the lines,the method, during an end of the start-up, comprising: injecting thereductive nitrogen compound from the reductive nitrogen compoundinjector into at least one of the lines flowing to the boiling waterreactor at an increasing quantity; injecting the alcohol from thealcohol injector into at least one of the lines flowing to the boilingwater reactor at a constant quantity; wherein no hydrogen is providedfrom the hydrogen injector into any of the lines; wherein the reductivenitrogen compound and the alcohol are injected during the end ofstart-up such that a reducing environment characterized by anelectrochemical potential higher than −300 mV is provided in the boilingwater reactor.
 14. A method for operating a nuclear power plantincluding a boiling water reactor, lines flowing to the boiling waterreactor, a hydrogen injector for injecting hydrogen into at least one ofthe lines, an alcohol injector for injecting an alcohol into at leastone of the lines and a reductive nitrogen compound injector forinjecting a reductive nitrogen compound into at least one of the lines,the method, during a beginning of a normal operation of a hydrogen waterchemistry or noble metals chemistry addition, comprising: injectinghydrogen from the hydrogen injector into at least one of the linesflowing to the boiling water reactor, injecting a reductive nitrogencompound from the reductive nitrogen compound injector into at least oneof the lines flowing to the boiling water reactor and injecting analcohol from the alcohol injector into at least one of the lines flowingto a boiling water reactor, wherein the alcohol is injected at aconstant quantity as the hydrogen is injected at an increasing quantityand as the reductive nitrogen compound is injected at a decreasingquantity; wherein the hydrogen, reductive nitrogen compound and thealcohol are injected during the beginning of the normal operation of thehydrogen water chemistry or noble metals chemistry addition such that areducing environment characterized by an electrochemical potentialhigher than −300 mV is provided in the boiling water reactor.
 15. Themethod as recited in claim 1 further comprising: compensating foreffects on electrochemical potential during on-line noble metalschemistry addition injection by increasing the alcohol injected.
 16. Themethod as recited in claim 1 further comprising maintaining anelectrochemical potential higher than −300 mV.